When the sample is processed by using the plasma formed in the processing vessel as described above, such factors as a temperature distribution in a direction across the sample holder which carries the sample placed thereon during the processing, the density distribution of the plasma, and the distribution of reaction products decrease uniformity of processing across the surface of the sample, which presents a problem. As conventional means for solving the problem, a technology for controlling the temperature distribution across the surface of the sample holder and thereby adjusting the temperature distribution across the surface of the sample such that the processing is performed uniformly has been proposed.
An exemplary conventional technology is disclosed in Japanese Patent Laid-Open No. H 9(1997)-17770, which provides plural systems of refrigerant channels in a sample holder to provide a non-uniform temperature distribution across the sample holder and thereby render the temperature of the sample uniform (Prior Art Technology 1)
There has also been known another conventional technology disclosed in Japanese Patent Publication No. 2680338, which locally varies the pressure of a gas supplied to the back surface of the sample and thereby renders the temperature of the sample uniform (Prior Art Technology 2).
Although each of the foregoing prior-art technologies has examined a structure for controlling the temperature distribution across the surface of the sample, they have the following problems.
Since the prior art technology 1 requires a long time from the time the refrigerant temperature is changed until the sample temperature is changed and stabilized, it presents a problem when a plurality of different processes are performed individually on a per step basis with respect to a single wafer on a single sample holder. If each of the processes is not initiated until the temperature is stabilized, the time during which the processes are not performed increases so that the overall processing efficiency lowers. If each of the processes is initiated by the time the temperature is not stabilized, on the other hand, another problem is encountered that the process cannot be performed with high precision.
In addition, the prior art technology 1 has not considered the mutual thermal influence between the portion of the sample closer to the center thereof and the portion of the sample closer to the outer periphery thereof even in the case of performing a process which requires a large difference between the respective temperature values of the portion closer to the center and the portion closer to the outer periphery. Consequently, the temperature varies gradually so that a desired temperature distribution is not provided.
The prior art technology 2 adjusts heat transfer between the sample and the sample holder by varying the pressure of a gas for heat transfer supplied to the back surface of the sample under processing at desired positions on the back side of the sample and thereby suppresses fluctuations in temperature across the surface of the sample in a shorter period of time. However, since it is impossible to adjust the temperature only when heat is inputted from the plasma to the wafer, a predetermined temperature distribution cannot be obtained if heat supplied from a stably formed plasma and from a member in the processing vessel under the influence of the plasma varies greatly till it reaches a normal state and if the processing time is short. In the case of performing a process which requires a large difference between the respective temperatures of the portion of the sample closer to the center thereof and the portion of the sample closer to the outer periphery thereof, if the amount of heat from the plasma is small, the temperature distribution that can be provided is limited so that it is difficult to produce a large temperature difference.
It is therefore an object of the present invention to provide a plasma processing apparatus capable of adjusting the temperature of a wafer in a wide range and processing a sample to be processed with high precision.
Another object of the present invention is to provide a plasma processing apparatus which allows a desired temperature distribution to be realized within a wafer in a shorter period of time and thereby performs processing with higher efficiency.